The following website analysed the effect of so-called isotonic exercise on
strength:
http://www-rohan.sdsu.edu/dept/coachsci/vol51/housh.htm
<< DCER (Isotonic) Training Improves Strength And Its Retention In Trained
And Untrained Limbs
Housh, T et al. (1995). Effects of eccentric only resistance training and
detraining. International Journal of Sports Medicine, 17, 145-148.
The effects on dynamic constant eccentric resistance (DCER - formerly called
isotonic training) training on the extensor muscles of one leg were assessed
for: eccentric DCER strength in both legs, concentric isokinetic leg
extension peak torque-velocity curves in both legs, and retention of the
previous two factors after detraining.
Males were divided into a training group and a non-training control group .
Training consisted of eight weeks of eccentric-only DCER exercise (3-5 sets
of 6 repetitions at 80% of eccentric 1 RM) on the nondominant limb followed
by an additional eight weeks of detraining.
DCER strength improved in the trained (29%) and untrained (17%) limbs. No
changes in isokinetic values were recorded in either limb. The training
increases were retained after eight weeks of detraining.
Implication:
DCER (isotonic) training involves considerable neuromuscular skill
development. It is known that initial strength training effects are neural
(skill changes) and so it is not surprising that training "effects" are
retained when development starts from an initially low level. This type of
neural development also explains the "cross-training" effect to the untrained
limb. Another explanation might be changes in everyday limb-use that
stimulated development in the untrained limb. >>
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*** This article and its accompanying analysis warrant some careful
dissection.
REDEFINITION OF ISOTONICS
The parenthetical definition of "DCER - dynamic constant eccentric
resistance" training as the correct modern term for "isotonic" training is
fraught with errors and inaccuracies. First of all, it is entirely
tautological to use the adjective "dynamic", since eccentric exercise is
always dynamic. There is no such entity as static eccentrics. Really! It
sounds something like the tautology I heard on some TV weather report which
referred to the "coastal seaboard" - are there any seaboards that are not
coastal?
Next, it is totally incorrect to equate any form of eccentric training with
isotonic training, since the old concept of "isotonic" (constant muscle
tension) training, however inaccurate it may have been, was applied to a full
movement or series of movements and not just the eccentric phase of those
movements. "Isotonic" training referred to allegedly constant muscle tension
exercise in a movement comprising both concentric and eccentric phases, so it
is mystifying how any scientists could deviate so from the original meaning
of the concept of "isotonic" action. As a matter of historical interest, who
actually decided to coin the term "DCER (Dynamic Constant Eccentric
Resistance) as a substitute for "isotonic"?
Why was concentric action left entirely out of the picture and why, for that
matter, did the creators of that neologism not call "isotonic" training as
DCCR (Dynamic Constant Concentric Resistance) training, or even DCCER
(Dynamic Constant Concentric-Eccentric Resistance) training? Maybe they
realised that, in all non-cyclical movement, there is also an isometric phase
between each concentric and eccentric phase.
Certainly, most of us are aware that it is virtually impossible to maintain
constant muscle tension over any extended range of joint action and that the
term "isotonic" should have been discarded or carefully qualified many years
ago, but to replace it with DCER is equally inappropriate.
After all, two quite acceptable and non-controversial terms have been widely
used in Europe and Russia for many years, namely "auxotonic" and
"allodynamic", which referred to exercise in which muscle length and tension
were varying all the time. Even the rather more generic term "dynamic" would
have been preferable to "DCER".
Now let us address the concept of "constant eccentric resistance".
"Isotonic" exercise did not refer to exercise against constant resistance,
but to exercise which presumably implicated constant muscle tension.
Constant muscle tension is very different from constant external resistance.
Anyhow, even if constancy of resistance is the qualifying condition that the
researchers intended to use, its application to the real world of exercise is
highly questionable, because it requires special machines to ensure constancy
of external resistance throughout the full range of any joint movement. This
condition of constancy of eccentric resistance using conventional weights or
pulley machines simply does not happen over any extended range of joint
movement.
Possibly this sounds unduly critical, but the reviewers of any article which
unquestioningly accepted DCER as the appropriate synonym for "isotonic"
surely must have carried out a very cursory evaluation of the original
submission. Possibly they were far more interested in the statistical
methods and laboratory procedure, rather than in the essential biomechanical
and physiological issues under consideration. Maybe they really did not
fully appreciate the field that they were called upon to analyse, in which
case they should have recused themselves from the review process.
Whatever the case may be, the exercise science community needs to appreciate
that this latest attempt at renaming "isotonic" training is seriously
inaccurate and should not be adopted as the standard definition in any
publications or teaching situations.
MAXIMAL ECCENTRICS?
The experiment stated that "Training consisted of eight weeks of
eccentric-only DCER exercise (3-5 sets of 6 repetitions at 80% of eccentric 1
RM)". How, may I ask was the eccentric 1RM (single repetition) maximum
obtained for each test subject? One often reads that concentric action is
the least 'strong' of all types of action, while eccentric action allows one
to move something like 30-40 percent more than one's concentric maximum, but
nobody has yet defined incontrovertibly what a true eccentric maximum is. We
can estimate this by defining it to be the maximum load that we can lower
against gravity over a period of not less than 3 or 5 seconds, but this
actually implicates an element of local muscle endurance and not simply
discrete 'strength'.
Such measurements of maximum eccentric strength apparently prove that
eccentric strength is greater than maximum isometric strength, which, in
turn, is greater than maximum concentric strength. Now, maximum isometric
strength is the utter limit strength that the muscles can produce to prevent
a load from overcoming voluntary muscle effort, then maximum eccentric
strength must be strength that one can exert to exceed one's voluntary
maximal strength. This must then imply that maximum eccentric strength takes
the muscles close to their mechanical limits. Of course, one presumes that
the Golgi Tendon Organ Reflex fortunately reduces any potentially dangerous
production of muscle tension before maximum tension and structural failure
occur.
This sounds fairly convincing until one notes that the muscle tension
produced during a voluntary maximum eccentric phase of carefully controlled
weight training movements very often is significantly less than rapidly
amortised involuntary eccentric actions, such as those which occur when one
drops from a height. So, as our eccentric tale unfolds, does this now
suggest that a more realistic measurement of maximal eccentric strength has
to be made under involuntary, very rapidly terminated eccentric movements?
Despite all this further speculation, the measurement of a maximum maximorum
(maximum of all maxima, as my colleague Dr Zatsiorsky aptly describes it in
his "Science and Practice of Strength Training", 1995) under eccentric
conditions still remains as elusive as ever. So, we have to ask if it is
entirely realistic and even possible to meaningfully measure maximum
eccentric strength in any given joint movement.
Now, if we return to the publication that stimulated this discussion, how did
the researchers manage to establish accurate 1 RM (Rep Max) measurements of
eccentric knee extension-flexion so that their experiment would produce
scientifically valid results?
Dr Mel C Siff
Denver, USA
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